The present invention relates to a control system for controlling engine-operated accessories of an automobile.
Automobiles having automatic gear transmissions including fluid couplings such as torque converters are liable to move slowly in the forward direction, a phenomenon called "creep", due to a fluid drag when the automobile is stopped, unbraked, with the gear shift lever in the D range. The creep is undesirable since fuel economy upon engine idling is lowered and idling vibration is increased especially with front-engine front-drive automobiles.
There have heretofore been proposed and put to use many creep prevention devices which automatically place the gear transmission in the neutral position in response to detection of the idling running condition of the automobile.
The creep prevention device is generally arranged such that it will operate only in the low gear range to prevent engine braking from being impaired since the gear transmission is placed into the neutral position by the creep prevention device. Alternatively, the creep prevention device may be arranged to operate only when the automobile speed is lower than an extremetely low reference speed such as of 10 km/h.
This means that in the second gear range or higher gear ranges, or at automobile speeds higher than 10 km/h, the creep prevention device is not operated, and the engine braking is effective, allowing the engine torque from being transmitted to the drive wheels.
Various automotive accessories driven by the engine, such as an air conditioner compressor, consume a large amount of energy upon operation. Therefore, a device called an "opener" is added for increasing the throttle opening in synchronism with operation of the compressor. The opener is set to a relatively large opening in order to maintain a desired cooling capability. As a consequence, the idling speed of the engine at the time the compressor is in operation is higher than the idling speed when the compressor is at rest by a speed range from 100 to 200 rpm.
Therefore, even if the accelerator pedal is allowed back to the idling position in the second gear range or higher gear ranges, or at automobile speeds higher than 10 km/h, in which the creep prevention device is not operated, the creep-induced torque is increased by the operation of the compressor, making the automobile body vibrate to a greater extent.
While the automobile is being decelerated to a stop, the rotational speed of the drive wheels is initially high to enable the drive wheels to drive the engine (engine braking), and no large vibration is applied from the engine to the automobile body through the engine mount system. When the automobile speed is lowered and the automobile approaches a stop, the drive wheels are then driven by the engine, and the engine mount system is caused to flex, thereby transmitting vibration from the engine to the automobile body. With an automatic gear transmission having four forward gear positions, for example, such large vibration is induced immediately before gears are shifted from top to third gear positions, from third to second gear positions, and second to low gear positions. The vibration is largest in level at the time of a downshift from the second to low gear positions with a large gear ratio, and smallest in level at the time of a downshift from the top to third gear positions.